java时间操作

import java.util.Date;
import java.util.Calendar;

import java.text.SimpleDateFormat;

public class TestDate{
public static void main(String[] args){
Date now = new Date();
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");//可以方便地修改日期格式
String hehe = dateFormat.format( now );
System.out.println(hehe);

Calendar c = Calendar.getInstance();//可以对每个时间域单独修改
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int date = c.get(Calendar.DATE);
int hour = c.get(Calendar.HOUR_OF_DAY);
int minute = c.get(Calendar.MINUTE);
int second = c.get(Calendar.SECOND);
System.out.println(year + "/" + month + "/" + date + " " +hour + ":" +minute + ":" + second);
}
}

有时候要把String类型的时间转换为Date类型，通过以下的方式，就可以将你刚得到的时间字符串转换为Date类型了。

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");

java.util.Date time=null;
try {
time= sdf.parse(sdf.format(new Date()));

} catch (ParseException e) {

e.printStackTrace();
}

Calendar c = Calendar.getInstance();
int hour = c.get(Calendar.HOUR_OF_DAY);
int minute = c.get(Calendar.MINUTE);
DateFormat df = new SimpleDateFormat("HH:mm");
Date d1 = df.parse("11:31");//字符串转日期
Date d2 = df.parse("11:30");
long diff = d1.getTime() - d2.getTime();//这里diff是一个长整形数,如果d1比d2靠后，就是正数，比如本例就是正数，反之为复数，相等为0
System.out.println(diff);